1. Field of the Invention
The present invention relates generally to a flow measuring device including an A/D conversion circuit that converts a flow voltage signal, which is an output signal from a flow rate detecting part, into digital data and outputs the data. In particular, the present invention relates to a flow measuring device for an internal combustion engine.
2. Description of Related Art
A flow measuring device measures the amount of suction air of an engine for an automobile, for example. The flow measuring device includes a flow rate detecting part for detecting a flow rate of air passing through a flow passage, and outputs an output signal in accordance with the flow rate. This output signal fluctuates due to influence of the flow of air. Accordingly, there is a technology that performs averaging processing on the output signal to reduce the influence of the fluctuation of the output signal upon rotation fluctuation and torque fluctuation.
For example, it is described in JP-A-H11-159393 that an air flow rate is calculated based on an output signal from a flow measuring device, and that smoothing processing of the output signal from the flow measuring device is performed only during idle operation. As a result of this technology, accuracy in flow detection by the flow measuring device at the time of idle operation is improved. However, at times other than idle operation, if an unstable air flow is generated near the flow measuring device in the case of a large air flow rate, the output signal of the air flow rate is fluctuated, and rotation fluctuation and torque fluctuation may thereby be affected. Nevertheless, measures against this are not taken.
The present applicants have invented a technology that A/D converts and outputs a voltage signal (flow voltage signal) that is outputted from a flow rate detecting part in accordance with the flow rate of air inside the flow measuring device, and a technology that shortens a sampling period of A/D conversion for the flow voltage signal (see Japanese Patent Application No. 2010-107330).
In such a flow measuring device, data outputted from the flow measuring device may be loaded on an engine control unit (ECU), and then averaging processing may be performed thereon in the ECU. However, since the ECU loads the data of the flow measuring device with a predetermined period, if the sampling period of A/D conversion for the voltage signal is short, the ECU cannot load all the data, and accuracy of averaging is reduced, so that the flow detection accuracy may become low.